M31[2], the giant Andromeda galaxy, is a near twin to our own galaxy, the Milky Way. Both are spiral galaxies, and they’re about the same size and mass. And each has a supermassive black hole at its center.

The black holes themselves aren’t exactly twin-like — the one in Andromeda is probably 10 to 20 times as massive as the one in the Milky Way. But the environments around the black holes are similar — each is encircled by a cluster of bright young stars.

Astronomers recently confirmed the cluster at the center of M31. It spans several light-years, and contains hundreds of stars. Many of those stars are hotter and brighter than the Sun, indicating that they’re also more massive than the Sun.

Such stars can’t be very old. In fact, the cluster may be just 100 million to 200 million years old, compared to an age for the overall galaxy of more than 10 billion years. The cluster may have formed when a giant cloud of gas collapsed around the black hole, breaking up into smaller clumps that made individual stars. Today, these stars provide a bright contrast to M31’s dark heart[2].

M31 is in good view on winter evenings. Tonight, it’s about two-thirds of the way up the western sky at nightfall, not far from the upper right corner of the Great Square of Pegasus. Under dark skies, it’s visible to the unaided eye as a small, hazy smudge of light — the light of a galaxy that’s much like our own.